This invention relates to a method of restoring a picture through estimation, in which a picture is read by sampling it in relatively low picture element concentration and is restored as a picture higher in picture element concentration.
In general, in a digital type copying machine or in a facsimile equipment, an original picture is scanned by a scanner to provide electrical signals, which are converted into digital signals by an analog-to-digital converter, so that the picture is sampled according to its density levels. That is, the picture is read as the density levels of picture elements forming the picture.
In this connection, in order to simplify a reader adapted to read a picture and to reduce the capacity of a transmission path used in digitally transmitting video signals, the number of bits per picture element is reduced by sampling an original picture in a relatively low picture element concentration, so that the picture is read in a relatively low picture element concentration. The picture thus read is reproduced as a picture higher in picture element concentration by a suitable processing means so that the reproduced picture is improved in quality. The processing means is, for instance, a calculating means such as an electronic computer. The processing means operates to estimate through simulation how the input picture is varied when reproduced, so that the resolution of the picture whose picture element concentration is relatively low as described above is improved. In this estimating operation, the most important thing is how accurately the curves in the original picture was reproduced.
In a conventional method of this type, an original picture is divided into square picture elements in relatively low concentration, and the picture elements are sampled to provide white and black level data, so that the picture is represented by bits, i.e. a binary picture is provided, and a picture higher in picture element concentration is reproduced from the binary picture. In this case, in order that the curves of the original picture are reproduced as smooth curves, a particular picture element is divided into four minute picture elements, and the density levels of the minute picture elements are statistically determined white or black from the density level data of the particular picture element and those of the picture elements surrounding the particular picture element (cf. Japanese Patent Laid-Open No. 41115/1978).
However, if an original picture is sampled in 4 picture elements/mm.times.4 picture elements/mm and is restored in 8 picture elements/mm.times.8 picture elements/mm according to the conventional method described above, then it is difficult to reproduce the curves in the picture as satisfactorily smooth curves; that is, the resolution of the reproduced picture is inadequate (cf. FIG. 5).